In the recent past, orthopedic casts formed from materials other than the theretofor conventional plaster of paris have found increasing acceptance. Usually, such orthopedic casts employ a carrier or bandage coated with a material that can be temporarily softened while the bandage is wrapped about the affected body portion, say a limb, and which thereafter hardens. Alternatively, such bandages may be used in conjunction with materials that are hardened by applying physical agents (such as ultraviolet radiation, ultrasound or heat) or chemical reactants to them.
One particularly successful orthopedic bandage, marketed by the assignee of this application under its trademark HEXCELITE, utilizes a carrier having relatively large openings (defined by a fabric of widely spaced apart strands) to which a heat softenable polymer composition is applied. A length, say six feet or more of the bandage is wound into a roll and the roll is immersed in heated water. After the entirety of the roll has reached the desired temperature so that all of the polymer composition is heat softened, the roll is removed from the water and the bandage is unwound about the person's limb to form the orthopedic cast. When the temperature of the compound with which the carrier is impregnated falls below its softening temperature the cast rigidifies.
The resulting cast exhibits excellent strength, abrasion and impact resistance. Yet it is much lighter than conventional plaster casts and other prior art casts. Further, the large openings defined by the carrier permit good air access to the underlying skin to prevent skin maceration.
In addition to having the proper wearing characteristics, materials from which orthopedic casts are made must, of course, lead themselves to being formed into a cast. This requires that the material must be quickly available for forming it into the cast and that it harden promptly while leaving sufficient time so that it can be formed or molded into the cast. Additionally, the material must not cause discomfort or injury due to such factors as excessive heat, poisonous or noxious substances and the like.
Heat softenable orthopedic bandages such as the one marketed under the trademark HEXCELITE percent a twofold problem. First, the bandage roll convolutions must be prevented from adhering to each other when the polymer composition is heat softened or the bandage cannot be conveniently applied. Secondly, the bandage and in particular the polymer composition should heat up quickly when placed in a heating medium, typically a heated water bath. Once the heated bandage is removed from the bath, however, it should remain in its softened state for a sufficient length of time, preferably for six or seven to 10 minutes, to enable the molding of the cast before the polymer composition cools to below its softening temperature and hardens. The desired quick heating and slow cooling of the bandage, however, are not entirely compatible because one normally precludes the other. For example, in the case of HEXCELITE bandages, which typically have bandage openings of around 0.025 in.sup.2, the immersion of a 2-3/4 in. roll in water of 165.degree. F. requires only about 1/2 minute to heat it up. However, the roll, once removed from the bath, cools to below the softening temperature of the polymer composition in as little as five to 51/2 minutes, often an insufficient time period for forming a cast.
To overcome both the problem of bonded bandage convolutions and a short cool down period orthopedic bandages such as the one marketed under the trademark HEXCELITE, as well as others, employ "release films" that are placed between the convolutions of the bandage roll. These release films prevent an adherence of adjacent bandage convolutions when the roll is heated and further slow down the cooling rate of the roll once removed from the heated water bath so as to give the person forming the cast sufficient time to fully apply the bandage. A drawback of such release films is the fact that they significantly prolong the time required for fully heating the bandage roll because they greatly inhibit water circulation through the roll. However, since the bandage often cannot be effectively applied unless the bandage roll remains in its heat softened, pliable state for substantially more than five minutes, say seven to 10 minutes, the drawback of prolonged water submersion times was accepted as the lesser of two evils, particularly since the release film significantly reduced the heat loss and, under the conditions of the above example, typically prolonged the available time to form the heated bandage into the orthopedic cast to well in excess of 10 minutes.
Prior art patents which demonstrate the present state-of-the-art in regard to bandage material for forming orthopedic casts as discussed above include the following U.S. Pat. Nos.: 3,420,231; 3,763,858; 3,935,355.